1. Field of the Invention
The present invention generally relates to improvements in a radar system and, more particularly, to an improved clutter tracker in a moving target indication (MTI) radar system.
2. Description of the Prior Art
Different MTI radar systems are known in the art. Such systems are capable of extracting the echo or returns of a moving target from the echo of clutter, even though the clutter echo may be many fold greater in amplitude than the moving target echo. This is accomplished by tracking the clutter and removing, or at least minimizing, its effect on the display on which the real targets are indicated. Various techniques have been employed to cancel the effect of stationary clutter. Some systems have also been developed to track moving clutter and cancel its effect in a fully automated MTI radar system, in which target indication signals are automatically produced, in order to minimize the number of false target indication signals.
In one such system, sometimes referred to as "TACCAR" for time average clutter coherent airborne radar, average doppler velocity of moving clutter is measured for clutter cancellation. In this system, if the clutter velocity changes in range, the system tracks the geometric mean of the observed clutter velocities. Consequently, the system yields unsatisfactory results in environments in which clutter of different velocities, such as ground clutter, rain and chaff are encountered. Also, the system is relatively slow and therefore it cannot be used effectively with a step scan radar.
In another system, which has been proposed, although some clutter is cancelled, the leading and trailing edges of the clutter are not cancelled. Consequently, a fairly high rate of false target indications are produced, i.e., a fairly high false alarm rate occurs. Various clutter gating schemes have been tried to alleviate this problem. However, to date such schemes have only met with very limited success.